Re: [rp-ml] STL files

From: Delft Spline Systems <>
Date: Wed Dec 06 2006 - 18:39:25 EET

Hi Adrian,

Thanks for the comment, and of course you are absolutely right that the Euler formula was long known, and could have been somehow 'built in' the STL file definition. And then the STL file would cause less problems for all slicing algorithms that aren't sufficiently robust to handle gaps.

However: this would not have solved the problem but only have shifted it: in that case surface modellers like Alias and Rhino would not have been able to export STL files easily. From my point of view the current STL file is ideal as any 3D CAD program can easily write one, and as incompatibility problems do not exist because of its simplicity. I can understand though that from a different point of view STL is not so ideal.

I just wanted to also illuminate the positive side of STL, as that absolutely is present too.

Best Regards,

Lex Lennings.

At 13:22 06-12-2006, Adrian Bowyer wrote:
>>I would say that refusing to build is a problem of the RP software, not of the STL data format.
>Not really. This is a GIGO effect. If a solid object being described by its surface has a gap in that surface (for example) then it either has zero volume, or it occupies the entire Universe. (Or rather the whole of Euclidean Space, which is bigger, even if it is a fiction...) Of course software can sometimes patch this up, but for any given patch-up algorithm it is inevitable that - sooner or later - that "sometimes" will fail.
>This was a problem with a known simple solution when the STL format was defined. As that solution had been around since the time of Poincaré (1854 - 1912), if not Euler (1707 - 1783), that is a bit annoying. It's the sort of thing that happens when you let mechanical engineers (like me) define a data structure...

Delft Spline Systems, The Netherlands.
We offer DeskProto: affordable Rapid Prototyping using CNC milling. --- website:
Received on Wed Dec 06 17:19:42 2006

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